Electric furnace resistor



Patented May 29, 1923.

PATENT orifice.-

H, PENNSYLVANIA, ASSGQTQ'R T.) WESTINGHOUSE ELECTRIC & MANUFACTURINGCOMPANY, A CORPORATION OF PENNSYLVANIA.

ELETEHC FNACE RESISTE.

Application filed May 24,

T o all whom it may concern:

Be it known that I, GEORGE M. Lrrrnn, a citizen of the United States,and a resident of Pittsburgh, in the county of Allegheny and State ofPennsylvania, have invented a new and useful Improvement in ElectricFurnace Resistors, of which the following is a specification.

My invention relates to electric furnaces and particularly toelectric-resistance furnaces, and it has for its object to provide abuilt-up resistor comprising a plurality of relatively large andrelatively small carbonaceous elementsl resiliently compressed in thefurnace chamber'.

In my co-pending application. Serial No. 454,776, iled March 23, 1921, Ihave disclosed an electric-resistance furnace ink which the heatingelement comprises a plurality of integral carbonaceous elements.

The resistance of a heating element of the above-described character is'relatively low, thus requiring a source of energy ot' relatively lowif'oltage and relatively high current capacity to energize the heatingelement to maintain the relatively liigli 'temperature desired. rlhelosses in the contact terminals and in the current leads are relativelyhigh, and it isdcsirable to increase the resistance of the heatingelement in order to obtain the saine temperature in the furnace chamberwhen using a smaller current. l

In practicing my invention, I provide a resistor which comprises aplurality of fiat carbonaceous plates alternating with a plurality ofrelatively narrow thin strips of the same material. The compoundresistor is maintained in its operative position in the 'furnace chamberby means of ay resilient co1npressing means of sul'istantially thecharacter described in the hercinbefore mentioned application, The areaof the plates and the area and number oi' the narrow strips aredetermined in accordance with the desire i kilowatt input or" thefurnace.

In the single sheet of drawings:

Figure 1 is a view, in vertical cross section, of an electric-resistancefurnace comprising the device embodying my invention:

- Fig. 2 is a view, in side elevation, of one of the flat plates of theresistor upon which are mounted a plurality ci thin strips. and y Fi 3is a view, in end elevation, of the mem ers illustrated in Fig.

An electricl furnace com s t .itin

.resilient compressing means may 1921. Serial No. $2,092. Y

framework or casing 11, provided with suitable Supporting members 12.Outer walls 13 comprise a plurality of bricks or blocks of a suitableheat-insulating material. Inner walls 111 comprise a plurality of bricksor blocks of a suitable high-temperature resisting material. The walls111 are spaced apart to provide a furnace chamber 15 of any suitable ordesired contour and dimensions. As the furnace is to be employed inheatving metallic articles, an opening 16iis provided in one of thewalls, near the bottom of the chamber, to permit of introducing andremoving the articles.

A heating element 17, which is located in the furnace chamber. comprisesa plurality of relatively large flat carbonaceous plates 18 alternatingwith a plurality of relatively narrow, elongated strips 19 also made ofcarbonaceous material. As illustrated in the drawing, the narrow strips19 are preferably placed transversely of the large plates 18 for areason to be hereinafter set forth more in detail. End members 2O ofgraphite are provided, one or" the members 20 being located against oneof the inner walls 14. The other end member 20 is adapted to beoperatively engaged by an elongated carbonaceous electrode 21, extendingthrough one of the side walls of the furnace into the furnace chamber.

A watercooled metallic contact terminal 22 is provided with a conicalaperture which is adapted to be located on the tapering outer end of theelectrode 21. In order to insulate the contact terminal 22 from themetallic framework of the furnace, an insulating member 23 is located inthe outer face of the furnace wall immediately surrounding the terminal22.

In order to resiliently compress the builtup resistor 1'?, I provide athreaded screw 24 and a helical spring 25. The inner end of the helicalspring 25 engages an insulating member 26 placed between the .end of thespring and the outer face of the Contact terminal 22. `While I haveillustrated a specic resilient compressing means, I desire it to beunderstood that such means is illustrative only and that any suitable ordesired be venlployed.

As they temperatur of the inner end ofz the .electrode 21 is relativelyvery high, the tempesatura er the electrode inside of the walls land 14is also relatively high and, if 'unprotected, would be oxidized byentering air. To protect the electrode over that portion of its lengthlocated in the walls 13 and lll, l provide a well or hopper 27 in whichis placed a mass 28 of granular carbonaceous material .which surroundsthe electrode 2l over a portion of its length. Air flowing along theouter surface ot the contact terminal 22 encounters the mass of granularmaterial, and expends its oxidizing efl'ect thereon. This arrangement ismore fully described and claimed in my co-pending application Serial No.4721093, iled May 24, 1921.

It is well known that the resistance of a column of resilientlycompressed fiat carbonaceous plates is relatively very low. By placing arelatively small number of narrow strips of carbonaceous materialbetween two adjacent flat plates, I find it possible to materiallyincrease the resistance of the resistor. This result is, obtained otcourse, because of the contact resistance-existing between the narrowstrips and the fiat plates and Ialso because of the very large decreaseof contact area traversed by the current. l preferably use three narrowstrips, locating them to extend transversely ot' the large plate-andsymmetrically disposed thereon. Thev 'center line of pressure exertedagainst the built-up resistor by the electrode is so located as to be'between two of the symmetrically-disposed narrow carbon strips.

The plates are`- so placed in the furnace chamber that the Sides havingthe longer dimensions are in a substantially vertical position. Thenarrow strips l!) are. therefore, in substantially a horizontal positionand I find this arrangement advantageous preventing the entering` airfrom oxidizingthe upper portion of the flat plates and the upper twonarrow strips. ln case oxidation vis effected by the entering air, thelower edge ofthe flat plates and the bottom strip are attacked but thebuilt-up resistor is still "maintained in its operative position in theurnace", by reason of the tact that the center line oftcomprcssiou islocated between two upper narrow strips.

I have found lthat the amount ot current which may be caused to traversea built up resistor of the above indicated lcharacterA Imay easily beregulated by varying either fthe number of the narrow strips or byvarying the area thereof. It is, of course, apparent that an increase ineither the number of strips or ot' the area of the strips reduces theresistance and, therefore, permits a greater current to liow When theresistor is connected to a source of energy of a given voltage.,

The ,resistor illustrated in the .drawing vspaced-apart comprises twoparallel parts substantially of the character described in thehereinbefore mentioned application. However, this is not an essentialfeature, as only one of such parts may be used, in which case terminalelectrodes are located in oppositewalls of..

the .furnace instead of in the saine wall.'

lt may be noted that the device embodying my invention provides arelatively simple built-up resistor, the resistance ot' which may beeasily varied in accordance with the desired kilowatt input of the'furnace. It may be noted also that this type of resistor provides arelatively simple means for varying the resistance either by a change inthe number of connecting strips or in the area of such strips.'

Various modifications may be made in the device embodying my inventionwithout departing from the s irit and scope thereof and I desire that ony such limitations shall be placed thereon as are imposed by the priorart or are specifically set forth in the appended claims.

l claim as my invention:

' l. An electric-resistance furnace comprising a built-up resistor'consisting of single flat carbonaceous plates of relatively large areaot cross-section alternating consecutively with a plurality of flatcarbonaceous plates ot relatively small area of cross seetion, the areaot' cross-section ot' the small plates being in accordance with thekilowatt `input of the furnace.

2. An electric-resistance furnace comprising a built-up resistor ofalternating plates otcarbonaceous material of relatively large area ofcross-section and a plurality ot' narrow elongated bars of carbonaceousmaterial, each oi said bars extending laterally of Said large plates andmeans for compressing said built-up resistor, the center line ofcompression being located between two of said bars and above the centerof gravity of the area of the large plate.

3. An electric-furnace resistor comprising flat carbonaceous plates ot'relatively large varea of cross-section, and a plurality of relativelynarrow carbonaceous bars of relatively small area of cross-sectionlocated between adjacent plates ofA large area.

d. An electric-furnace resistorcomprising flat carhonaceous plates ofrelatively large area ot cross-section and a plurality of relativelynarrow carbonaceous bars of relatively small area of cross-sectionlocated in plates of large area.

In testimonywhereof, I have hereunto subscribed myname this 18th day ofMay,

iaei.

l esoneri M. Lrr'rtin.

relation betweenadjacentV Gli

